Optical angle measuring apparatus



April 15, 1952 D R 2,592,543

OPTICAL ANGLE MEASURING APPARATUS Filed Feb. e, 1946 2 SHEETSSHEET 1 5/ FIG. I g

Z? 4% w A I? .5 a7 I Z7 H" 7 April 15, I952 J. DAUBER OPTICAL ANGLE MEASURING APPARATUS 2 SI-IEETSSHEET 2 Filed Feb. 6, 1946 FIG-.2.

Patented Apr. 15, 1952 OPTICAL ANGLE MEASURING APPARATUS Joseph Dauber, Chicago, 111., assignor to Acme Scientific Company, Chicago, 111., a corporation of Illinois Application February 6, 1946, Serial No. 645,926

Claims.

This invention relates to optical measuring apparatus, and with regard to certain more speciflc features, to an optical sine bar for measuring angle tapers.

Among the several objects of the invention may be noted the provision of simple apparatus for measuring tapers or angles of bodies capable of manifesting either intended or unintended tapered or angled wedge shapes, such as cones, pyramids, prisms, cylinders and the like; the provision of means for measuring deviation from a specific taper; and the provision of apparatus of this class which has means for determining initial error within the apparatus itself. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

Fig. 1 is a perspective view of the invention;

Fig. 2 is a top plan View;

Fig. 3 is a front elevation of Fig. 2;

Fig. 4 is a right-side elevation of Fig. 3;

Fig. 5 is a longitudinal section taken on line 55 of Fig. 6, and shows a roll-supported angle block or sine bar;

Fig. 6 is a bottom plan view of Fig. 5;

Fig. '7 is a detail section showing means for handling bulged cones; and,

Fig. 8 is a detail view of the angle block of Fig. 5 but showing an alternative form of work holder.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Referring now more particularly to the drawings, numeral I shows an accurately flat metal base, such as a tool makers flat. This is preferably chromium plated, at least on its upper surface 3, and provides one of the optically fiat surfaces desired. On the fiat upper side of this base is located cylindric support 5, having a vertically thread shank 9 operable up and down by turning it. The shank 9 has a rounded support ing nose H providing a single-point support. For accurate adjustment the shank 9 is provided witha fine male thread 8 at its lower end which is an accurate fit in a corresponding female thread ID in the lower portion of the support 5.

To assure that the threads fit without backlash, the threads on 9 are in the form of a tap. Upon insertion of the tap into the previously roughedout female threads in member 5, this tap performs a finishing tapping operation, thereby generating a female thread which fits it exactly. The remainder l2 of the shank 9 is accurately lap fitted to the unthreaded upper portion of the bore in 5, which makes the shank 9 substantially free from shake during adjustment. A thumbscrew 1 is provided to clamp the shank 9 against inadvertent further rotation, once a desired height has been attained.

' At numeral I3 is shown an angled block supported upon accurately made rolls l5 and IT. This assembly I3, I 5, I! may also be called a sine bar. The block i3 has an optically flat upper surface [9. It is recessed at what becomes its lower end, as shown at 2|. This provides rightangular supporting portions 23 for accurate tangent contact with a central cylindric part 25 of the roll IS. The ends 2'! of the roll 15 are of equal size and larger than the central cylindric part 25. It should be noted that the beveled portion 29 between the right--angular portion 23 does not touch the part 25.

Toward the other end the angle block I3 is recessed as shown at 3|. The sides of this recess provide right-angular portions 33 for contacting gudgeons 35 on the second roll l1. Beveled portions 39 between the pairs of right-angular portions 33' do not touch the gudgeons 35. The roll l! is provided with a central integral disc extension M which is located within the recess 31 and clears it. Parts 21 and 4| are accurately the same size, as are also the parts 25 and 35.

The angle block i3 is attached to the parts 35 and 25 by means of angle screws 24 (Fig. 3). The end portions 27 (of roll l5) and portion ll (of roll ll) will act as a three-point support. The collar portions 21 and 41 should be accurately finished circles such that a plane passing tangentially to the three of them is accurately parallel with the optically flat upper surface I9 of block On the top surface is of the block it are a pair of lateral stop pins 43 and also an end stop pin 5, for aligning a conical work piece such as 41. The stop pins 33 are adjustable by means of eccentric extensions as below the surface l9, which enables the pins 13 to be adjusted so that the cente: inc of the work may be made to lie, as accurate. desired, in the normal plane of the dihedral angle determined the inclined be lowered in Fig. 4.

3 member l3. A bracket 49 carries an adjustable set screw which may be locked in position by lock nut 53. By means of the pins 43 and 45 and the screw 5|, the conical part 41 may be held on the optical fiat IS with one of its conical elements lying thereon. The axis of the work 41 should be in a plane substantially perpendicular to the axes of the rolls l5 and H.

A block 55 attached to the optical flat 3 forms an abutment for the cylindric portion 25 of the roll l5 (see Figs. 1, 2 and 3).

At numeral 51 is shown a gage block which is wrung to the flat 3. The height of this gage block 51 is such that when the collar 4| rests thereon, while the collars 21 rest on the flat 3, the angle of the upper surface I!) of the block will be such that the upper conical element of the work 4'! will be horizontal when its lower conical element rests upon said surface l9, provided the work is accurate. A spring 59 simultaneously presses collar 4| against the gage block 51 and the cylinder 25 into the angle between stop block 55 and the surface 3.

At numerals 5| are gage blocks in a stack, the bottom one of which is wrung to the base flat 3, the blocks also being otherwise wrung together. The total height of the stack of flats 6| is to be .001 to .002 inch or so lower in height than the upper conical element of the work 4?. The long dimensions of the fiats are substantially parallel to the long dimension of the block l3. This is accomplished by aligning them with a flat portion M on the otherwise cylindric support 5 which is parallel to said long dimension.

At numeral 63 is shown a glass optical flat. This is at least optically flat on its bottom and it rests upon the upper significant conical element of the work as shown at 65. Since the stack of gage blocks BI is slightly lower than the bottom of the optical flat 63, the latter will, in addition to resting upon the work, rest upon one edge 61 of the gage block stack, provided that the nose II is initially sufliciently below the level of the top of the gage blocks, as it should be at this time. This condition is not shown in Figs. 2-4 of the drawings but can be readily visualized by considering the nose H to Consequently, if the assembly be viewed in a monochromatic light, such as for example, from a helium lamp, a series of interference bands will appear parallel to the long edge 61 of the gage block. These are shown at l2 in Fig. 1. Viewed from above, these bands appear through the optical flat 63.

The height of the point H is then adjusted until point makes contact with the bottom working surface of the optical fiat 63 and lifts said flat. The flat, it will be recalled, rests upon the upper element "5 of the work 41. The bands l2 immediately become disturbed and as elevation proceeds, these bands l2 gradually shift angularly. Elevation is stopped when they are at right angles to their former positions, as shown at |fi in Fig. 2. In this position the bands are parallel to the short sides 69 of the stac of blocks 8|. The existence of these bands |6 indicates a lack of parallelism between the bottom plane of the optical fiat 63 and the top of the uppermost gage block 6| in the direction parallel to t e length of the blocks BI and block l3. It therefore also indicates a lack of parallelism between the element 65 of the work 41 and the plane of surface 3. Since the an le of the b10k 3 'h en ch n k work were of correct angle the element 65 would be parallel to the plane of surface 3, it may be assumed that under the stated conditions wherein the bands l3 show, the angle of the work is incorrect. In other Words, adjustment of the point until the parallel lines It appear, establishes the angle of the bottom plane 20 of the optical flat 63, and hence the angle of the element 65, relatively to the surface 3.

The number of bands is a measure of the inclination of the bottom of the optical flat 63 with respect to the horizontal plane of the top of gage blocks 6|, and consequently, it is also a measure of the inclination of the upper element 65 of the work from the nominal value.

As an example, let the specified tolerance of the taper on the work i! be 1.005 inch in 6 inches. If the upper gage block BI is 1% inches long (see edge 61) the stated taper amounts to .000115 inch in this length of the block. Since each interference band under the monochromatic helium light represents a deviation of .0000116 inch, it will be seen that the work will be about or within tolerance if ten or fewer bands appear on the gage block surface.

If the work is exactly correct in angle, no bands will appear across the gage block. This is also true when the work is very far out of limits, but the existence of a correct condition for measurement is revealed by the fact that bands appear if the optical flat is lightly touched so as to bring the surfaces of the optical fiat 63 and of the stack 6| slightly out of parallel. Since bands can be readily seen when the inaccuracy cf the angle is ten times as great as permitted, this factor presents no real difliculty.

It often occurs that the conical surface of a piece such as G1 is not only off-angle between its ends, or two chosen points on it, but that it is bowed between the ends. For example, it may be curved either with a bulge or a constriction. If the curvature is in the form of a bulge this means that the work 41 may rock on the surface lEl, and also that the optical flat 63 may rock on the element 55 of work. This makes measurement difficult because of sensitivity. However, this sensitivity reveals hitherto often unsuspected defects in the pieces. Whether the defect is a bulge or concave cavity may readily be detected if the work piece has a fairly high finish, or can be provided with such a finish without changing its shape. The latter method consists in illuminating with sufiiciently monochromatic light the point of contact of the work piece with the overlying optical fiat, and examining it with a microscope of appropriate magnification. The interference bands thus seen are, as usual, the measure of the departure of the surface from a true cone. In addition it may still be desirable to obtain a measure of the overall taper included between two definite points, even in the presence of bulging curvature. For this purpose fixtures may be employed having provision for placement of accurate wires 13, of equal sizes disposed as shown in Fig. '7. These wires may for example be accurate to within .00001 inch. The lower pair rest upon the surface I!) and the upper ones support the optical flat 63. The work piece 31 is located between the pairs of wires. The measurement then made as above described will indicate taper deviation between the points on the work at which the members of the upper and lower sets of wires contact.

In Fig. 8 is shown another method for holding the work on the block I 3. In this case an arm 15 is held in place on the block I3 by means of a thumbscrew 11 passing through an eye 19 and threaded into the block [3. The end of the arm has an overhanging head 8i. Shims 83 beneath the eye 19 control the spacing of head 8! from surface [9. Then by pushing the work under the head 81 with or without the Wires 85 (wires shown in Fig. 8), the head will slightly spring the arm 15 so that the work will be properly held. The head 8| presse: against the inner wall of the work piece 47 downwardly and diagonally toward the pins 43 in order that the work may be simultaneously pressed against both the pins 43 and the lower wires 85.

Any slight deviation of the axis of the work out of the plane of the vertical angle formed by the inclined bar does not affect the accuracy substantially. Thus misalignment of the order of Ky results in a maximum permissible angle error of measurement (due to the misalignment), which error for most work is negligible. And, errors of alignment of a half degree or so are readily detectable by the eye and are therefore easily avoided.

In use, the equipment requires about five minutes (time) for very accurate measurement of a piece, including the time for several rechecks. The device is versatile in its wide range of applications.

The initial angular error of the sine or angle bar 13 may be checked. This is effected by making its upper polished surface optically fiat within some specified limits. It is then placed with its rolls on a glass or quartz optical flat of adequate diameter. A second optical flat is supported about .002 inch above the sine bar by three equal stacks of gage blocks resting upon the said quartz optical fiat. The upper fiat should then be parallel to the lower flat. If the upper surface of the sine bar is then parallel to the plane upon which the rolls rest, it will also be parallel to the upper optical fiat, and when viewed in a monochromatic light no interference bands will appear. If, however, the upper surface of the sine bar is not parallel to the plane upon which the rolls rest, the amount of non-parallelism will be indicated by the number of interference bands which will appear, or by the spacing between them. The apparatus for checking as described is not shown in the drawings because it is the same type that would be used for checking for parallel surfaces on other optical flats or gage blocks. The point is mentioned, however, since it indicates the importance of the optically fiat characteristics of the upper surface I!) of the bar I3. It also calls attention to the importance of the requirement for parallelism between the surface 19 and a plane tangent to the bottoms of the circles of 21 and 4|.

It is to be understood that although the application uses as an illustration the measurement of a deviation from prescribed value of the external taper of a hollow piece in the shape of a truncated cone, other types of tapering work may be accommodated with suitable adaptations of the holding fixtures.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. Optical angle measuring apparatus comprising a block which is optically fiat on its top, a'plurality of supports for said block, a base member having an optically fiat upper surface supporting at least one of said supports, a first gage block means resting upon said last-named surface and supporting at least another one of the supports for holding at an angle the flat top of said block, means on said block for supporting a piece of conical work, an adjustable support on said base member, at least one additional gage block means resting on said surface of the base member and located between the work and said adjustable support, a transparent member having an optically flat bottom surface resting upon said work and upon said adjustable support, the spacing between said additional gage block means and the optically fiat bottom of said transparent member being small enough to produce interference bands visible through the transparent member.

2. Optical angle measuring apparatus comprising a block which is optically fiat on its top, a plurality of circular supports for said block, the block having means on its underside for'engaging said supports, the effective diameters of said supports being such that a tangent plane touching all of them beneath the block will be parallel to said optical fiat top, a base member having an optically flat upper surface supporting at least one of said circular supports, a gage block resting upon said surface of the base member and supporting the remainder of said circular supports, means on said block for supporting a piece of conical Work on its fiat top, an adjustable support on said base member, at least one additional gage block means resting on the base member and located between the work and said adjustable support, a transparent member having an optically flat bottom resting upon said work and upon said adjustable support, the spacing between said additional gage block means and said optically fiat bottom being adapted to produce interference bands if the upper surface of the work and of said last-named gage block are not parallel.

3. Optical angle measuring apparatus comprising a base having an accurate fiat top, a gage block resting upon said top, a sine bar having an optically fiat top and supported upon the flat top of said base and the gage block to predetermine an angle of said optically fiat top of the bar. means supporting angled work on the angled flat top of the bar, a transparent optical flat, an adjustable single-point support on said bas for one portion of said optical flat, another portion of said flat resting upon the angled work, and at least one other gage block resting upon the top of said base and extending to a region close to the bottom of said optical fiat and located between said single-point support and the region of support of the fiat on the work.

4. Optical angle measuring apparatus comprising a base having an accurate flat top, a gage block resting upon said top, a sine bar having an optically fiat top and having roller supports upon the flat top of said base and upon the gage block to predetermine an angle of said optically flat top of the bar, means supporting conical work on the flat top of the bar with the axis of the work lying in a plane which is perpendicular to said flat top and also perpendicular to the axes of the roller sup-ports, a transparent flat having an optically fiat bottom, an adjustable single-point support on said base for the flat bottom of said transparent flat, another portion of said fiat bottom resting upon a line element of the conical work, and at least one other gage block resting upon the top of said base and extending to a point close to the bottom of said transparent flat.

5. Optical angle measuring apparatus comprising a base having an accurate horizontal fiat top, an angle block having an accurate fiat top, three supporting means for the angle block at least a portion of which rest upon the upper surface of the base, a gage block resting upon said upper surface of the base and supporting the angle block by the remaining supporting means and thereby controlling the angle of the upper surface of said angle block, means for holding conical work on the angle block with its axis in a plane normal to said flat top and normal to the upper surface of said angle block, the angle of the upper surface of the angle block being such that if the conical work were perfect an upper significant line element thereof would be parallel to the top of the base, additional gage block means resting upon the upper surface of the base adjacent the work and having an upper horizontal surfac slightly lower than said line element of the work an adjustable supporting means on said base, and a transparent fiat having an optically flat bottom 8 resting upon said line element and upon said adjustable support and extending over and adjacent to the upper horizontal surface of said additional gage block means.

JOSEPH DAUBER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,395,664 Benson Nov. 1, 1921 1,554,392 Weaver Sept. 22, 1925 1,901,632 Chamberlain Mar. 14, 1933 1,931,730 Klay Oct. 24, 1933 2,306,227 Seidel Dec. '22, 1942 2,325,904 Brabeck Aug. 3, 1943 2,351,773 Lovenston June 20, 1944 2,359,018 Balk Sept. 26, 1944 2,365,436 Saucier Dec. 19, 1944 2,376,959 Christel May 29, 1945 2,417,150 Berry Mar. 11, 1947 2,446,562 Trbojevich Aug. 10, 1948 FOREIGN PATENTS Number Country Date 710,881 Germany Sept. 23, 1941 

